Ring Lights are usually used by photographers who mostly shoot Macro Photography, however Studio Photographers do use Ring Lights too, however Studio Photographers Ring Lights are usually much bigger than the Macro Shooters. Ring Lights can be either Flash or Continuous light based.
Ring flashes (or ring lights) provide some awesome light. They are very common with the fashion industry where they are used to create a glamorous look.
The most common use for a small ring flash is to use it to create a subtle fill light. Since the light is coming from 100% on-axis, it has very little effect on the scene other than to provide additional light.